gistfile1.rbx

>> class Foo
>>   def initialize &block
>>     instance_eval &block
>>   end
>>   def const_missing const
>>     "foobar"
>>   end
>> end
=> nil
>> Foo.new do RandomConstant end
NameError: uninitialized constant RandomConstant
   from (irb):9
   from (irb):3:in `instance_eval'
   from (irb):3:in `initialize'
   from (irb):9:in `new'
   from (irb):9